From automotive technology it is known that with automatic transmissions having stepped transmission ratios a driving situation can arise, such that a maximum permitted motor speed is reached but too little power is available in the engaged gear. Owing to the lack of power the motor cannot generate the required traction force or the desired acceleration capacity needed for the next-higher gear step.
The driving situation described above is as a rule recognized by a driving strategy of an automatic transmission. As a result, in this driving situation an upshift is prevented. The frequency with which this driving situation occurs increases as transmission intervals per gear become larger, i.e. the driving situation occurs more frequently in transmissions with fewer gears, for example with six gears, than in transmissions with a larger number of gears, for example with 16 gears.
Due to the prevention of upshifts in such driving situations, the problem arises that the vehicle's motor is run for a longer time at the maximum motor speed. When the motor is running at full-load speed, its efficiency is lower. Consequently, the fuel consumption rises considerably. Moreover, the environment is affected adversely by larger quantities of exhaust gas emission and by greater noise production. In addition, driver acceptance is reduced since in the driving situation described, the driver is expecting an upshift.
For example, from DE 197 40 648 A1 a device for controlling gearshifts in an automatic transmission is known. In this device a means for preventing upshifts is provided, which only permits or carries out the upshift after a given time. When the current motor speed corresponds to the maximum motor speed, the upshift is prevented. However, as soon as the current speed tends to exceed the maximum speed, the upshift is initiated so that the motor speed will be reduced again. Thus, with the known device, exceeding the maximum motor speed is prevented because an upshift takes place.
Accordingly the problem outlined above, namely that of insufficient power in the next-higher gear, is not solved at all by the known device, since with the known device an upshift to the next-higher gear leaves the motor unable to provide the necessary traction force and the necessary acceleration capacity. Moreover, since with the known device operation at maximum motor speed is permitted, the fuel consumption also increases.